A number of different industries rely on impact grinders or hammermills to reduce materials to a smaller size. For example, hammermills are often used to process forestry and agricultural products as well as to process minerals, and for recycling materials. Specific examples of materials processed by hammermills include grains, animal food, pet food, food ingredients, mulch, and even bark. In many processing methods, whole grain corn must be cracked before it can be processed further. Dependent upon the process, whole corn may be cracked after tempering yet before conditioning. A common method to carry out particle size reduction is to use a hammermill, where successive rows of rotating hammer-like devices spinning on a common rotor next to one another comminute the grain product. For example, methods for size reduction as applied to grain and animal products are described in Watson, S. A. & P. E. Ramstad, ed. (1987, Corn: Chemistry and Technology, Chapter 11, American Association of Cereal Chemist, Inc., St. Paul, Minn.), the disclosure of which is hereby incorporated by reference in its entirety. The application of the invention as disclosed and herein claimed, however, is not limited to grain products or animal products.
Hammermills are generally constructed around a rotating shaft that has a plurality of disks provided thereon. A plurality of free-swinging hammers is typically attached to the periphery of each disk using hammer rods extending the length of the rotor. With this structure, a portion of the kinetic energy stored in the rotating disks is transferred to the product to be comminuted through the rotating hammers. The hammers strike the product, driving it into a sized screen, in order to reduce the material. Once the comminuted product is reduced to the desired size, the material passes out of the housing of the hammermill for subsequent use and further processing.
A hammer mill will break up grain, pallets, paper products, construction materials, and small tree branches. Because the swinging hammers do not use a sharp edge to cut the waste material, the hammer mill is more suited for processing products that may contain metal or stone contamination, wherein the product may be commonly referred to as “dirty”. A hammermill has the advantage that the rotatable hammers will recoil backwardly if the hammer cannot break the material on impact. One significant problem with hammermills is the wear of the hammers over a relatively short period of operation in reducing “dirty” products, which include materials such as nails, dirt, sand, metal, and the like. As found in the prior art, even though a hammermill is designed to better handle the entry of a “dirty” object, the possibility exists for catastrophic failure of a hammer causing severe damage to the hammermill and requiring immediate maintenance and repairs.
If rigidly attached hammers contact such a non-crushable foreign object within the hammermill assembly housing the consequences of the resulting contact can be severe. By comparison, free-swinging hammers provide a “forgiveness” factor because they will “lie back” or recoil when striking non-crushable foreign objects.
Hammermills also may be generally referred to as crushers-which typically include a steel housing or chamber containing a plurality of hammers mounted on a rotor and a suitable drive train for rotating the rotor. As the rotor turns, the correspondingly rotating hammers come into engagement with the material to be comminuted or reduced in size. Hammermills typically use screens formed into and circumscribing a portion of the interior surface of the housing. The size of the particulate material is controlled by the size of the screen apertures against which the rotating hammers force the material. Exemplary embodiments of hammermills are disclosed in U.S. Pat. Nos. 5,904,306; 5,842,653; 5,377,919; and 3,627,212.
The four metrics of strength, capacity, run time, and the amount of force delivered are typically considered by users of hammermill hammers to evaluate any hammer to be installed in a hammermill. A hammer to be installed is first evaluated on its strength. Typically, hammermill machines employing hammers of this type are operated twenty-four hours a day, seven days a week. This punishing environment requires strong and resilient material that will not prematurely or unexpectedly deteriorate. Next, the hammer is evaluated for capacity, or more specifically, how the weight of the hammer affects the capacity of the hammermill. The heavier the hammer the fewer hammers that may be used in the hammermill in light of the available horsepower. Accordingly, all else equal a lighter hammer increases the number of hammers that may be mounted within the hammermill compared to a heavier hammer. The more force that may be delivered by the hammer to the material to be comminuted against the screen increases effective comminution (i.e., cracking or breaking down of the material) and thus the efficiency of the entire comminution process is increased. In the prior art, the amount of force delivered is evaluated with respect to the weight of the hammer. Finally, the length of run time for the hammer is also considered. The longer the hammer lasts, the longer the machine run time, the larger profits presented by continuous processing of the material in the hammermill through reduced maintenance costs and lower necessary capital inputs. The four metrics are interrelated and typically tradeoffs are necessary to improve performance. For example, to increase the amount of force delivered, the weight of the hammer could be increased. However, because the weight of the hammer increased, the capacity of the unit typically will be decreased because of horsepower limitations. There is a need to improve upon the design of hammermill hammers available in the prior art for optimization of the four (4) metrics listed above.